This invention relates to a method for the adhesion of two silicon nitride parts.
Silicon nitride excels in strength, resistance to thermal shock, and resistance to chemicals. Because of these outstanding attributes, this compound is attracting attention as a new refractory material different in type from ceramics formed of metal oxides. Efforts are being continued to develop new uses for this compound in various fields.
Applicability of silicon nitride to the production of machines and tools for use at elevated temperatures, high-precision machine parts, heat exchangers, ceramic parts destined to be instantaneously heated to high temperatures, and thermal insulators for use in special circumstances is being studied.
In the production of such machines and tools as mentioned above, it often becomes necessary first to make their component parts and then to join them into finished products, for example. For successful assemblage of such silicon nitride parts of varying shapes, therefore, development of a method capable of providing fast adhesion of these component parts is a prime requisite.
Unfortunately, silicon nitride generally shows a very poor wetting property to molten substances and, unlike ceramics of oxides such as alumina and magnesia, possesses a strong covalent bond property and, therefore, has very low reactivity with other compounds. Since the thermal expansion coefficient of this compound is only about one half of that of alumina, adhesion of this compound is extremely difficult to obtain.
One common technique heretofore used to effect adhesion of two silicon nitride parts has resorted to the hot press method which carries out the adhesion in a hot press mold at elevated temperatures under high pressure. By this method, however, adhesion of silicon nitride parts of large dimensions or complicated shapes is obtained only with extreme difficulty because the operation is performed at high temperatures under high pressure. Even if such adhesion is obtained somehow or other by the hot press method, the strength of adhesion is not sufficient.
This invention has been perfected for the purpose of eliminating the aforementioned disadvantages suffered by the conventional method. It provides effective adhesion of two silicon nitride parts without entailing the harsh conditions of elevated temperatures and high pressure. By the method of this invention, these parts are joined with powerful adhesive strength as high as 800 kg/cm.sup.2. Their faces joined by adhesion defy breakage, enjoy ample chemical stability, and excel in resistance to heat and thermal shock.